Process for the production of metal borides and nitrides



T. E. O'CONNOR July 19, 196s PROCESS FOR THE PRODUCTION OF METAL BORIDESAND NITRIDES Original Filed Jan. 25, 1960 FIG.]

2O ANGLE l N V E ITOR TIMOTHY E. O'CONNOR United States Patent 2 Claims.(Cl. 23191) This is a division of application Serial No. 4,252, filedJanuary 25, 1960.

This application is a continuation-in-part of copending applicationsSerial No. 717,543, filed February 26, 1958, now abandoned; Serial No.744,006, filed June 23, 1958, now abandoned; Serial No. 744,680, filedJune 26, 1958, now abandoned; and Serial No. 789,518, filed January 28,1959, now abandoned.

This invention relates to boron nitride and i more particularly directedto turbostratic boron nitride and processes for its production.

In the drawings:

FIGURE 1 is a photomicrograph, at a magnification of 1000 diameters, ofturbostratic boron nitride particles produced according to thisinvention, after grinding. The insert in the upper left-hand corner is aphotomicrograph of crystalline boron nitride particles. The insert inthe lower right-hand corner is an artists representation of thelarnellae of turbostratic boron nitride, showing their lack ofthree-dimensional order; and

FIGURE 2 shows two superimposed graphs. The solid line represents theX-ray diffraction pattern of turbostratic boron nitride producedaccording to this invention. The broken line represents the X-raydiffraction pattern of crystalline boron nitride.

Her-etofore, boron nitride has been made by numerous methods, all ofwhich, however, have been quite costly, or have been technicallydifiicult to practice or have yielded relatively impure products. Amongthe commercial methods employed in the past have been those involvingthe heating of boron trichloride with ammonia at temperatures highenough to cause simultaneous breakdown of by-product ammonium chlorideto nitrogen, hydrogen, and hydrogen chloride, and the method of reactingboron trichloride with molten aluminum in the presence of nitrogen gas.In 1902, L. Moser and W. Eidrnann (Ber 35, 535; 1902) described thereaction of boric oxide and ammonia and although this process has beenfrequently studied in View of improvement, the physical properties ofboric oxide at the temperatures necessary to effect a reaction renderthe equipment design quite difficult and result in impure anduneconomical boron nitride. A marginal improvement has been obtained byusing boric oxide on an inert extraneous support such as tricalciumphosphate, carbon black, or preformed boron nitride, at elevatedtemperatures with ammonia. Most of these methods suffer from thedifficulty of securing boron nitride free of ionic or metallicimpurities at a moderate cost. The use of preformed boron nitride as asupport in the latter method gives a low production rate and requireshigh temperatures while the use of a support other than boron nitriderequires the subsequent removal of the support by aqueous or acidelution at a stage where the physical properties of the boron nitriderender it susceptable to hydrolysis. The separation of boron nitridefrom the latter type of support is further aggravated by the largeamount of support (up to four times the weight of the starting boricoxide) which must be removed. Methods such as these are likely to giverise to the generation of ionic impurities which mitigate against theuse of the boron nitride as an electrical insulator.

Because of the importance of boron nitride as an electrical insulatorand high frequency dielectric over a very wide temperature range, as anatomic reactor structural material and neutron shield, as a material ofconstruction for components of rockets and supersonic aircraft, as acomponent of pumps for handling certain molten metals, and as a hightemperature lubricant, a significant need has arisen for cheaper andmore efficient methods for manufacturing boron nitride.

In 1869, it was reported by H. Darmsta'dt (Liebigs Annallen der Chemie,151, 255 (1869)) that boron nitride can be obtained by heating boricacid with urea and washing the resulting mixture with aqueoushydrochloric acid. Further experience with the method of Darmstadt aswell as some of the above-mentioned methods indicated that only fractionyields (up to 28%) of boron nitride of substantial impurity could beobtained by these methods (Ullmann, Enzyklopadieder Technische Chemie,Aufiage 2 p. 542). Recently a product which analyzed 27.2%

boron and 22.6% nitrogen was obtained in a yield of.

quire an extraneous support for the reacting boron com-.

pound.

It has been discovered in accordance with this inven-.

tion that boron nitride of high purity can be manufactured efficientlyand at relatively low cost by heating boric acid with certainnitrogenous materials and removing volatile by-products, at least thefinal portion of the heating being conducted in the presence of addedamonia in the absence of any extraneous supports. More particularly theinvention provides a process for manufacture of boron nitride whichcomprises heating boric acid with at least one nitrogenous materialselected from the class consisting of urea, biuret, triuret, cyanuricacid, ammelide, melamine, thiourea, guanidine, aminoguanidine,cyanamide, dicyandiamide, semicarbazide, and thiosemicarbazide, removingwater and any other volatiles, and with at least the final portion ofthe heating being conducted in the presence of added ammonia in theabsence of any extraneous support. In the preferred embodiment, theinvention provides a process for manufacture of boron nitride whichcomprises heating orthoboric acid with at least one of the compoundsselected from the class consisting of urea, cyanamide, dicyandiamide,thiourea, biuret, and guanidine in a mole ratio of 1 mole of boric acidper 1 to 2 moles of the above-mentioned compounds, at a temperatureusually not exceeding C., removing water from the reaction zone duringthe ensuing condensation by applying subatmospheric pressure thereuponuntil more Patented July 19, 1966.

than about 60% of 2 moles of water per mole of boric acid employed isremoved, followed by additional heating of the condensation productabove 150 C. but preferably not exceeding about 400 C, removingadditional Water and other volatiles from the reaction during theheating preferably in the absence of molecular oxygen (e.g., in a streamof ammonia or other carrier gas such as nitrogen) until the residue isconverted into a solid, agitating said solid and adding ammonia eitherin combination with or in the absence of an inert carrier ga when thetemperature exceeds about 400 C. and further heating the intermediatesolid to about 700 C. to 1000 C., whereupon the intermediate solid whichis formed above 400 C. is converted to substantially pure boron nitridein good yield.

The processes of the invention have numerous advantages over those ofthe prior art. It does not require the use of extreme temperatures at astage in the process wherein corrosive materials are encountered.

A distinctive feature of this invention is that the intermediateresidues which are formed at temperatures above 400 C., and which areammoniated to boron nitride are solids and require no supports toenhance their conversion to white boron nitride, which is substantiallyfree of ionic impurities and, in fact, contains minor amounts of oxygenas the only significant impurity. These intermediate residues consistessentially of the combined elements boron, nitrogen, and oxygen,although in some instances minor amounts of carbon and hydrogen arepresent; in these cases these elements are removed as volatile productson heating to higher temperatures (600 C). In the preferred embodimentof this invention the atomic ratio of nitrogen to boron present in theintermediate residues generally lies between 0.3 and 0.7.

Although the exact structures of these intermediates are not known, theyare believed to be substantially selfsupporting, solid, porous matricesof the combined elements, boron, nitrogen, and oxygen. The intermediateresidues of this invention readily react with ammonia at temperaturesabove 350 C. to give boron nitride and water. Furthermore, the extent ofconversion of the intermediate oxygenated boron residue to boron nitrideincreases with temperature, and boron nitride compositions with anitrogen content above 54% N have been obtained at a final maximumreaction temperature of 900 C. Thus, the practice of this invention,using these intermediate residues, leads to a pure boron nitriderequiring no further substantial purification and furthermore achievesthis object at moderate temperatures with consequent substantial savingsin cost of reactor equipment.

Still further advantages of the process of the present invention are asfollows: (1) generally no washing step is involved; (2) the startingmaterials are such that they are inexpensive when in pure form; (3) thinfilm techniques which involve removal of product from supporting solidsare eliminated; (4) yields are exceptionally high.

The mole ratio of boric acid to the second compound or compounds whichare employed in the practice of the invention is generally close to 1:1.An excess of the second compound is frequently helpful. The excessshould not be so large as to involve a wastage of the second compoundand excessively long reaction times to convert the materials to a solid.About 1-2 moles of the second compound per mole of boric acid arepreferred. Less than 1 mole of the second compound per mole of boricacid can be employed but is less advantageous since the intermediatesolid which is formed in the heating at about 400 C. is an oxygenatedproduct which adheres to the reactor walls.

In some instances (e.g., when urea or thiourea is used) the initialproduct may be a condensation product which may still be liquid at thelower portion of the temperature range (around 130 C.) but upon furtherelimination of volatiles during heating, the material becomes a friablesolid and remains as a solid throughout the remainder of the reaction.When the condensation product is transformed to the intermediate solidand the reaction is essentially complete as evidenced by reduction inthe rate of evolution of volatiles, the material is heated above 400 C.in the presence or" ammonia. In the preferred manner of condensing thecomponents at a relatively low temperature, the undesirable reaction ofthe decomposition of the organic nitrogenous material and theselfcondensation of boric acid is held to a minimum. The removal ofwater and other volatiles is preferably accomplished at subatmosphericpressure below C. and by the use of an inert gas sweep (e.g., nitrogen,carbon dioxide, or helium) between 150 C. and 400 C. The heating of theintermediate solid above 400 C. in the absence of ammonia does notresult in its conversion to pure boron nitride but results in a residualintermediate containing boron, nitrogen, and up to 50% by weight ofoxygen. The preferred method of ammonia addition is recited above;however, ammonia has been used in place of the gas sweep in thetemperature range of about 150 C. to 400 C. and may be used during theentire heating period.

Organic nitrogenous materials which are operable in the presentinvention include urea, biuret, triuret, cyanuric acid, ammelide,melamine, thiourea, guanidine, aminoguanidine, semicarbazide,thiosemicarbazide, cyanamide, dicyandiamide, ammeline, and salts of theappropriate foregoing with volatile acids. As is well known, some of theabove materials can be converted to salts by reaction with volatile ornonvolatile acids. It is considered desirable to use salts of theorganic nitrogenous materials, which in the practice of the invention donot leave a residue of ionic impurity in the final boron nitride such asthose derived from volatile acids. By the term volatile acid is meantany acid with a boiling point less than 400 C. at atmospheric pressureor an acid which upon :-eating to less than 400 C. is decomposed leavingsubstantially no ionic residue. Generally volatile acids are those whichmay be removed by heating during the formation of the intermediate solidin the process of this invention. Obviously, the salts which are formedfrom the above acids should condense with boric acid under theconditions of the instant process. It is believed that nonvolatile acidssuch as sulfuric acid and phosphoric acid may be used but areundesirable in that ineificient washing procedures may be required forthe removal of the ionic impurity resulting therefrom. Alkyl and arylsubstituted derivatives of the above-mentioned group of nitrogenousmaterials are also operable, but in some instances are less desirable inthat their use may lead to the deposit of elemental carbon in the finalproduct.

Boric acid as used herein includes orthoboric acid, metaboric acid,pyrobo'ric acid, and condensed boric acids. When it is desired to formthe final boron nitride at a temperature below 1000 C., orthob oric acidis preferred. Somewhat higher a m moniation temperatures may berequ-ired when the other forms of boric acid mentioned above are used inthe initial reaction and may require that final temperature be in excessof 1000 C. Commercial ureas are definitely operable in the process ofthis invention and are included in the term. urea as used herein. Thesecommercial iu ne as may contain quantities of urea selfcondens-ationproducts and possible trace impurities peculiar to the particularprocess used in the manufacture of the urea. One skilled in the artrecognizes that at elevated temperatures ammonia exists in a reversibleequilibrium with nitrogen and hydrogen and that the extent of theequilibrium may be affected by the presence of certain catalysts.(Chemical Elements and Their Compounds, Sid'gwick, vol. 1, page 658.)Such gaseous mixtures are included in the term ammonia as used herein.

The boron nitride produced by the process of this invention has atunbostratic structure. The term turbostratic, as is well understood bycrystallograprhers, describes a layered structure in which successivelayers show random mutual orientation.

It is well known in the art that boron nitride is a poly-- mericmaterial. Physically, the material has a layered structure consisting ofstacks of lamellae. Each lamella consists of tused borazene rings. Such!a stack of lamellae is sometimes referred to as a parallel layer group.There is partial or complete mutual orientation of the lamellae in theparallel layer groups of the boron nitrides produced by processes knownheretofore. These materials possess partial or completethree-dimensional order. Boron nitride exhibiting this order is herereferred to as crystalline.

Boron nitride produced according to this invention, however, shows acomplete lack of three-dimensional order among its lamellae.Crystallographic studies, using Xaray techniques, to be moreparticularly described be low, show that while the boron nitride of thepresent invention has significant amounts of parallel layer groups,composed of stacked lamellae, there is zero probability of mutualorientation among successive lamellae in these stacks. This isillustrated by the lower right-hand insert of FIGURE 1 of the drawing.The layers or disks in the insert represent lamellae composed of fusedboraz'ene rings. It will be seen that these lamellae, while frequentlysuperimposed to form stacks, show no regular mutual orientation amongsuccessive lamellae in any stack. The term turbostratic is intended todefine a boron nitride exhibiting this lack of three-dimensional order.

In the present state of the crystallographic art, the assignment of aturbostratic structure to the boron nitride of the present invention isbased on an examination of its X-ray diffraction pattern and acomparison of this pattern with the diffraction pattern of crystallineboron nitride.

The samples were investigated at ambient room temper ature by Xray(infraction techniques, using the standard diffractorneter method inorder that the profiles as well as peak positions of the diffractionpeaks be recorded. This method is set out in X-ray DiffractionProcedures for Polycrystalline and Amorphous Materials, by H. P. Klugand L. E. Alexander, Wiley 1954.

The standard paratocusing reflection arrangement of the diffractometerwas used with copper radiation and nickel foil at least 0.001 inch thickfor a filter. Dilfracted radiation was detected by a flow proportionalcounter using argon, and the radiation intensity was recordedautomatically on a strip chart recorder as a function of 26, where isthe Bragg angle. Pulse height selection served to furthernronochromiatize the diffracted radiation. Powder samples were mountedin the usual manner in standard aluminum sample holders. The sampleswere compacted in the holders in such a way that the sample facepresented to the incident X-ray beam was smooth, flat, and flush withthe holder surface. The samples were at least 1.5 mm. thick andcompletely intercepted the incident beam throughout the selected Braggangle range.

The description of the diffraction patterns is limited to 26 anglesbetween 10 and 58 which is a range sufiicie-nt to characterize thesamples.

Referring to FIGURE 2, it will be seen that the X ray diffractionpattern on? turbostrat-ic boron nitride, represented by the solid line,shows two significant and broad diffiraction peaks, with peak positionsat approximately 25.0 and 42.4" in 20 units. The widths of these twomajor peaks may be described by the angular width at /2 maximumintensity and in this case were approximately 58 and 3.8 in 20 units forthe peaks at 250 and 42.4", respectively. The relative integratedintensity of the peak at 25.0 was 2.76 times larger than the relativeintegrated intensity of the peak at 424.

With further reference to FIGURE 2, it will be seen that the diffractionpattern of a crystalline boron nitride, represented by the broken line,shows within the designated angular range five very narrow and intensediffiraction peaks having positions of maximum intensity at approxi- 6mately 26.75", 4l.59, 43.84, 50.13 and 55.09, respectively. The halfmaximum widths of the peaks at 26.75 41.59, 43.8 4", 5 0.13, and 55.09"were approximately 0.39", 0.28", 0.31", 041, and 039, respectively. Theintegrated intensities of these peaks were approximately 63, 85, 32.2,81.7, and 44.3, respectively.

Table I shows the d-spacings and corrected relative intensities of thiscrystalline boron nitride.

TABLE I.-CRYSTALLINE BORON NITRIDE 11,1; 1 20 (1(A.) F2 11, k, 1

002 26. 75 a. 330 674 41. 50 2. 75 101 43. 84 2. 05s 16 102 50. 13 1.s20 57 004 55. 09 1. 667 225 where k:0.9 (for Le determination) or 1.84(for La determination), c=1.542 A., and B is the contribution to thehalf maximum breadth of diffraction peaks by instrumental factors. La iscalculated using 0 (100) and the half maximum breadth (B) of the (100)peak. L0 is calculated using 0(002) and the half maximum breadth (B) ofthe (002) peak. La and Lc are usually interpreted in crystallographicanalysis as average crystallite dimensions along the a and c unit celldirections. In the case of boron nitride La may be considered as anaverage layer diameter of the stacked layers and Le may be con sideredas an average parallel layer group thickness. While the average parallellayer group parameters of the crystalline boron nitride material are notdeterminable with a high degree of accuracy from the data in Table I, Laand Le have values in excess of A. when allowance is made forinstrumental broadening.

Table II presents the d-spacings and average parallel layer groupparameters of a typical preparation of turbostratic boron nitride madeby the process of this invennon.

TABLE II.TURBOSTRATIC BORON NlTRIDE 11, k, 1 2a d(A) B l L(A) 002 25. 03.56 5.8 14= Lo 10 42. 4 2. 13 s. s 46=La The value of Le indicates anaverage of only 3 to 4 layers per random parallel layer grouping.

The turbostratic structure of the boron nitride of this invention isbased on the position of the diffraction peaks in the diffractionpattern, the relative integrated intensities of these peaks, and theapproximate coincidence of these peaks with the positions of the (002)and (100) peaks of crystalline boron nitride.

It has been shown theoretically and experimentally that forturbostr-atic materials, the peak positions (position of maximumintensity) of the two-dimensional (h, k) reflections are a function ofthe average diameter (La), the peaks being displaced toward larger Braggangle from the corresponding (h, k, reflection in the threedimensionally ordered material, the displacement increasing withdecreasing La values. The peak position of the (10) reflection in TableII relative to the (100) reflection of crystalline boron nitride (TableI) can thus be ascribed to the relative sizes of the layer diameters ofthese materials. The position of the (10) diffraction peak of theturbostratic boron nitride and its displacement relative to the (100)peak of the crystalline boron nitride gives a value of 40 A. for theaverage layer diameter using the formula of Warren. This La is inexcellent agreement 'with that given in Table II which was calculatedusing the /2 maximum breadth of the (10) peak and the Scherrer equationmodified by Warren wherein k=l.84 (see J. Applied Phys. 13 36477 (1942)for both methods). In calculating La as given in Table II, the smalleffect of instrumental broadening was neglected.

The diffraction peak profile of the (10) reflection of the turbostraticboron nitride is in close agreement with the peak profile, calculatedfor two-dimensional reflections from turbostra-tic materials, accordingto the general theoretical analysis of Warren, [Phys Rev. 59, 69398(1942)], and using La=40 A. and normalizing to the maximum intensity.This further confirms that the material of this invention is aturbostra-tic material.

In addition to the two peaks in the angular range considered, theturbostrati-c boron nitride also gives a weaker two-dimensional (11)reflection at greater angle than 20=58.

Some samples of boron nitride made by the process of this invention alsogive a diffraction pattern containing, in addition to the (002), (10),and (11) peaks, an extremely weak and extremely broad diffraction peakbetween the (10) and (11) reflections. This peak can be ascribed to the(004) reflection, i.e., the second order of the (002) peak, and canpossibly be theoretically ascribed to a smaller deviation from theobserved average interplanar spacing.

The turbostratic boron nitride differs from crystalline boron nitride inthe absence of detectable general (h,k, 1) reflections, i.e., in theabsence of reflections other than (001) and (h,k, 0) or (h,k)reflections. Specifically, the boron nitride of this invention is onewhose diffraction pattern shows no detectable diffraction peaks atapproximately 43.8 and 501 in 20 unit using CllKca radiation and usingthe experimental techniques described above.

The boron nitride of the present invention shows other gross differencesfrom crystalline boron nitride. As prepared by the processes of thepresent invention, the boron nitride is obtained as a White powder witha rough and gritty feel. When subjected to mild grinding, as forexample, with a pestle and mortar, the material fractures conchoidallyand the individual fragments then show the typical appearance ofconchoidally fractured particles and are quite translucent. Suchparticles are illustrated by FIGURE 1. In comparison, the particles ofcrystalline boron nitride, illustrated by the insert in the upperlefthand corner, are platelets, have more regular edges, are somewhatopaque, and have a talc-like texture.

Turbostratic boron nitride has the novel and unexpected property of notbeing converted to crystalline boron nitride by thermal annealing onheating to elevated temperatures in an inert atmosphere. In this itdiffers markedly from the boron nitride materials made by processesknown heretofore. The latter materials, as is well known in the art,gradually increase in degree of crystallinity through a thermalcrystallization process on heating to temperatures above 1000 C. andattain a high degree of crystallinity, as determined by X-raydiffraction techniques, on heating to about 1500 C. The boron nitride ofthis invention, however, can be heated in an inert atmosphere totemperatures of about 1700 C. before the material shows signs ofcrystallization, as evidenced by the presence of three-dimensionalordering or mutual orientation of the lamellae in the parallel layergroupings, as determined by X-ray crystallographic analysis by theaforementioned methods. In some instances, the boron nitride, as made bythe methods of this invention, can be heated to temperatures above 2000C. without showing evidence of crystallization. This is the case whenthe boron nitride has an atomic ratio of nitrogen to boron in excess of0.93. Such boron nitrides are readily 0btainable by the processes ofthis invention without the use of reaction temperatures in excess of1000 C.

When a turbostratic boron nitride, in which the atomic ratio of nitrogento boron is close to a value of 1.0, is heated to about 2000 C., eitherin an atmosphere of an inert gas or in a vacuum, the materialdissociates into its elements.

The turbostratic boron nitride of this invention can be furtherdifferentiated by its reactivity from the boron nitrides producedheretofore. Previously known boron nitride is an extremely inertsubstance and will withstand several hours contact with aqueoushydrochloric acid without decomposition. The boron nitride of thepresent invention, however, is hydrolyzed on addition to cold water,with considerable development of heat and the evolution of ammonia. Insome instances, the rate of heat evolution is great enough to heat thewater close to the boiling point. This hydrolysis was found to be about50 mole percent after a 3O1minute contact with boiling water.

The surface area of boron nitride prepared according to this inventionusually is in excess of about 40 m. /g., as measured by the standardnitrogen desorption method. In some instances a boron nitride with asurface area as high as -250 m. /g. is obtainable. This is particularlythe case when the preferred embodiment of the processes of thisinvention is employed, wherein the condensation of the boric acid withthe nitrogenous component to give the solid intermediates of thisprocess is effected under reduced pressure. In comparison, crystallineboron nitride has a surface area of 2.9-25 m. g.

Turbostratic boron nitride also differs from crystalline boron nitridein its displacement of n-hexane. Turbostratic boron nitride producedaccording to this inven tion displaces 1.721.78 grams of n-hexane percubic centimeter. In comparison, crystalline boron nitride displaces2.002.32 grams of n-hexane per cubic centimeter, and is clearly a densersubstance than turbostratic boron nitride.

Boron nitride as made heretofore is a refractory material. Much of theusefulness of this material until now was derived from its chemicalinertness. The boron nitride of this invention, however, has a highsurface area and a turbostratic structure containing parallel layergroups whose dimensions are minute by comparison with the parallel layergroups of crystalline boron nitride. Furthermore, the lamellae in theparallel layer groups of the turbostratic boron nitride are separated bya greater interlamellar spacing than in crystalline boron nitride, sothat this turbostratic boron nitride has a relatively open structure.

As a consequence of these structural features, the boron nitride of thisinvention reacts with a variety of metal oxides at temperatures above1000 C. to give a variety of metals, metal nitrides, and metal borides.The metal oxides which have been found reactive are the oxides of TABLEIII-REACTION OggfigggN NITRIDE WITH METAL Mole Ratio, BN Metal OxideMetal Oxide Temp, 0. Products Identified" Ni metal.

Mo Metal aMOzB MoB.

TELBz.

Unidentified, possibly LaBs.

It is to be noted that these reactions are unique in that many of themetal oxides which react with turbostratic boron nitride are normallyregarded as very refractory materials.

The preparation of aluminum nitride by heating a mixture of aluminumoxide and turbostratic boron nitride to a temperature of about 1500 C.provides a convenient and highly useful process for the preparation ofrefractory aluminum nitride in a state of good purity and is typical ofthis series of reactions. The reaction apparently involves adisproportionation at the reaction temperature with the formation ofaluminum nitride and volatile boric acid:

Since the boric oxide by-product boils at about 1580 C. at atmosphericpressure, it is readily removed from the system, suitable by sweepingthe reacting mass with nitrogen or an inert gas such as helium.

When the reaction is effected by heating the mixture of aluminum oxideand boron nitride in a rapid stream of nitrogen, the aluminum nitrideproduced is deposited as a mass of crystalline needles and plates on acold surface placed on the downward side of the gas stream from thereaction mass. It is desirable that such cold surface be at a lowertemperature than the reaction mass, but still be sufiiciently hot toavoid undue condensation of boric oxide. The cold surface can suitablybe constructed from solid, boron nitride ceramic or other refractorymaterial. Crystalline needles and plates with a maximum dimension ofabout 1 cm. are readily deposited and grown on such a plate.

Crystalline boron nitrides as made heretofore show only slight or noreaction on heating with aluminum oxide as described above.

The aluminum oxide used in preparation of aluminum nitride as describedabove is suitably any one of the pure grades of aluminum oxidecommercially available. Even refractory aluminum oxide, such as aluminumoxide which has been subjected to a roasting or firing operation at hightemperature is operable. Finely divided or colloidal aluminas andparticularly aluminas which have not been previously sintered atelevated temperatures show enhanced reactivity. It is desirable,however, that the alumina be free of water of hydration, since thelatter reacts with turbostratic boron nitride yield of aluminum nitride.

The aluminum nitride made as described above is essentially inert toattack by boiling water. In some instances, however, where the materialshows a detectable aqueous instability, the water resistance and generalrefractoriness of the material is further improved by heating andholding for some time at temperatures of about 20002200 C.

The aluminum nitride as made by the above methods is highly useful as arefractory, as an abrasive, and as a high temperature thermal insulatorand thermal radiation reflector.

The metal borides and nitrides produced according to this invention areuseful as refractories, abrasives, metal analogs with unusual electricaland thermal properties, and as metallurgical additives for theproduction of metal alloys. They are especially useful because they areobtained free of any appreciable metal carbide impurity.

The metal alloys formed by the addition of from 0.01% to 10% by weightof the borides or nitrides thus formed to metals such as iron, titanium,chromium, vanadium, and copper have outstanding hardness and toughness.

Alternatively, metals can be surface-treated by passing them through ametal nitride or boride powder, or they can be treated by packing thenitrides or borides around the metal and heating to a temperature ofabout 1600 C., the temperature depending upon the particular metal oralloy.

Turbostratic boron nitride can also be used for the surface treating ofa variety of metals and metal alloys. In this treatment, the metal ormetal alloy is heated while surrounded by the turbostratic boronnitride. The metal or alloy and the surrounding turbostratic boronnitride is heated to a temperature sufficiently great to secure surfacereaction of the metal or alloy with the boron nitride, with theresulting formation of a surface layer rich in metal boride and/ornitride. The presence of this chemically altered surface layer confersunusual hardness and toughmess on the metal or alloy body. Metals oralloys which are susceptible to improvement by this treatment consist ofor contain transition metals.

The turbostratic boron nitride of this invention can be used, inapproximately equivalent amounts, to replace part or all the carbon incarbon steels and various other iron alloys. The amount of turbostraticboron nitride used is generally about 2% of the total Weight of themetal.

The turbostratic boron nitride products of this invention can also beused in elastomers. The amounts and mode of use approximate those ofcustomary fillers such as carbon black and silica. The turbostraticboron nitride can be used with such elastomers as natural rubber, GRS,polybutadiene, polyisoprene, and other synthetic rubbers. Theturbostratic boron nitride may be used in amounts ranging from afraction of 1% to as high as 50% of the total weight of the elastomer.

The turbostratic boron nitride products produced according to thisinvention can similarly be used as fillers in such plastic compositionsas polyisocyanate, polystyrene, polyethylene, polyvinyl chloride,polymethyl methacrylate, polyacrylate, polyacrylonitrile, polyesterssuch as Dacron, and other polymers already well known. These plasticscan be in the form of fibers, films, foams, or sponge products. Theturbostratic boron nitride can be used in amounts ranging from 0.5% toas high as 50%, and can be used to replace part or all the customaryfillers.

It should be noted that when used in elastomers and polymers, asdescribed above, turbostratic boron nitride lends unexpected andvaluable strength to these products. This is attributable to the factthat the turbostratic boron nitride is quite active and cross-links suchproducts.

It has heretofore been quite difiicult to produce elemental boron ofhigh purity. Now, however, by using turbostratic boron nitride as astarting material, it is possible to obtain elemental boron of highpurity simply by and thus reduces the heating the turbostratic boronnitride to about 2000 C. as previously described.

, The following examples are intended to be illustrative only, and thecooling which is disclosed to facilitate pulverization between theindividual stages is not at all essential, since pulverization can beomitted or performed while the mixture is hot. All parts and percentagesare by weight unless otherwise specified.

Example 1 A mixture of crystal urea (600 g.) and orthoboric acid (309g.) was mechanically blended and then placed in a glass resin kettle.The resin kettle was equipped with an inlet for nitrogen gas, a paddlestirrer, and a vent connected to a water aspirator. The resin kettle wasthen heated with infrared lamps, placed to provide fully uniform heatingof the mixture. The mixture was melted, with slow stirring, over thetemperature range 6095 C. to give a homogenous nonviscous melt.Simultaneously water began to evolve from the melt. When the melt washomogenous, the pressure was reduced to 5070 mm. Hg by means of thewater aspirator, and the evolving water was rapidly removed. Over aperiod of about 1 hour, the temperature of the melt was raised from 95to 125 C. As the temperature was raised and the evolving water wasremoved, the viscosity of the melt gradually increased and ultimatelybecame sufficiently great to prevent stirring. Over a period of afurther hour the temperature was continuously increased. At about 145-160 C., the viscous melt was transformed into a white solid. Attemperatures above 145 C., ammonia and other volatiles evolved from thesolid and were removed by the water aspirator. A final temperature ofabout 320 C. was attained. At this stage the material in the resinkettle consisted of a friable, white solid. Heating was thendiscontinued, nitrogen was bled into the reactor, and the material inthe resin kettle was cooled in an atmosphere of dry nitrogen. Theresidue in the flask weighed 320 g.

Material from 4 runs, performed in the above manner, was mixed, ground,and thoroughly blended in a blender. The resulting blend (447.4 g.) wasthen placed within a 3'' OD, quartz tube, mounted vertically, and wassupported to form a bed, by a series of fused quartz chips. Dry ammoniagas was then passed vertically through the tube, at a rate of 2.2 litersper minute (S.T.P.). The ammonia flow fluidized the material in the bed.The quartz tube and its contents were enclosed by an electricalresistance furnace, which was used to heat the bed. The temperature ofthe fluidized bed after 1 hour of heating reached 450 C. At thistemperature, reaction of the ammonia gas with the fluidized bed resultedin the formation of water, which was removed in the eflluent gas stream.Over a period of a further 2 hours, the temperature of the bed wasraised to 900 C., and was then gradually increased to a finaltemperature of 1150 C. over a final period of 3 hours. The bed was thencooled in a stream of dry nitrogen gas. The resulting boron nitride(95.6 g.) was found on analysis to contain 43.2% B, 54.4% N.

The X-ray diffraction pattern of this material was that of turbostraticboron nitride.

Example 2 By means of a mortar and pestle, 60 parts by weight of ureaand 30.9 parts of orthoboric acid were intimately mixed together and90.2 parts of this mixture were placed in a Pyrex flask equipped with anexit tube leading through a condenser, cooled by Dry Ice, to a vacuumpump. The flask was heated, the temperature reaching 95 C. in 9 minutes.The pressure of the system was reduced to about 1 mm. of mercuryabsolute. At this temperature there was evidence of reaction, namely,condensation of water in the cooler parts of the system. During the next39 minutes the temperature was brought to222 C. During this time themixture became liquid, and about 16 parts of water were releasedtherefrom and were condensed on the cool surfaces of the system. As theheating continued, the viscous liquid was converted to a friablefoam-like solid, which amounted to 51.4 parts. A portion of the solid,4.1070 parts, was transferred to a quartz tube having an inside diameterof 1 inch, in which the solid was heated in a stream of nitrogen. Thetemperature was brought to 400 C. in minutes, with some condensateaccumulating at the cool end of the tube. Heating was continued from 400C. to 900 C. over an 80-minute period, with a stream of ammoniareplacing the stream of nitrogen. The material was held at about 900 C.for 50 minutes, whereupon the ammonia stream was stopped and the reactorcooled. Of the original charge of 4.1070 parts, 0.990 part was recoveredas white residue. The residue was pulverized and 0.966 part was returnedto the reactor, whereupon a treatment in ammonia at 900 C. was continuedfor 3 hours. A white residue, 095 34 part, corresponding to a 96.3%yield based on the boric acid employed, was recovered, which wassubstantially pure boron nitride (43.9% boron, 54.2% nitrogen).

The X-ray diffraction pattern of this material was that of turbostraticboron nitride.

Example 3 By means of a mortar and pestle 39.3 parts of biuret and 15.7parts of orthoboric acid were intimately mixed and placed in a Pyrexflask. The flask was then heated and when the contents of the flaskreached 65 C., there was evidence of reaction, namely, the condensationof water in the cooler portions of the flask. The temperature of thecontents of the flask was gradually raised to 123 C. over a 30-minuteperiod, whereupon the mixture in the flask melted, and the melt washeated further over a 50-minute period until the temperature of thecontents reached C., at which stage the residue in the flask had becomea white solid. This resulting solid was cooled by introducing a streamof nitrogen gas into the flask and 36.4 parts of the solid wererecovered from the flask and pulverized. Into a one-inch inside diameterquartz tube was placed 5.6700 parts of the pulverized solid and thequartz tube was placed in a tubular furnace. A means was provided at oneend of the quartz tube for the introduction of metered amounts ofnitrogen or ammonia gas and a means was provided at the other end toconduct the exit gas to a cold trap. The quartz tube was graduallyheated to 700 C. over a 35-hour period with a stream of dry nitrogen gaspassing through the tube. During this period, water and a whitesublimate evolved from the tube. Heating was continued for an additional2.5 hours at approximately 700 C. (tube wall temperature) withoutadditional formation of sublimate. The tube was then cooled and 1.1961parts of solid material were recovered which had a Kjeldahl nitrogencontent of 31.3%. A portion of this residue (0.9386 part) was replacedin the tube and the tube was heated to and maintained at approximately850 C. with a stream of ammonia gas passing therethrough for 5.5 hourswhence the furnace was cooled and the tube flushed with nitrogen. Of thecharge placed in the tube at the beginning of this step, 0.7889 part ofa white powder was recovered which analyzed 42.3% boron by sodiumcarbonate fusion and 48.2% nitrogen by Kjeldahl. The X-ray diffractionpattern of this material was that of turbostratic boron nitride. Triuretis also operable when used as shown in this example.

Example 4 Into a flask was added 38.06 parts of thiourea and 30.9 partsof orthoboric acid which has been mixed as in Example 3. The flask wasequipped with an exit tube leading through a condenser which was cooledwith Dry Ice and thence a vacuum system. The contents of the flask wereheated to 68 C. over a 15-minute period, whereupon Water evolved andthen over a 51-minute period the temperature of the contents was raisedto 153 C., whence the pressure in the system was reduced to 2 mm. Hgabsolute. The contents of the flask melted at 125 C. Heating wascontinued for 10 minutes at reduced pressure, during which time thematerial in the flask solidified and the temperature reached 160 C.Approximately 10 parts of water and 1 part of an immiscible liquid werecollected during the above heating cycles. Of the 53.6 parts of residuewhich were recovered from the flask after cooling, 10.2 parts of theresidue were mixed with 7.6 parts of thiourea using a mortar and pestleand 4.3351 parts of the resulting mixture was placed in a quartz tube asdescribed in Example 3. The tube was heated to approximately 700 C. overa 35-hour period in a stream of nitrogen gas. A slightly grey powder wasrecovered (0.7825 part) which analyzed 29.6% boron and 40.4% nitrogen.

A portion (0.4656 part) of the grey residue was readded to the quartzand heated between 730-850 C. for one hour in a stream of ammonia gas.After purging t-he tube and cooling as shown in Example 2, 0.3795 partof a white boron nitride was recovered which analyzed 40.3% boron and50.1% nitrogen. The X-ray diffraction pattern of this material was thatof turbostratic boron nitride.

Example According to the procedure of Example 2, 13.05 parts oforthoboric acid were mixed with 38.1 parts of guanidine carbonate. Thismixture, which was slightly sticky in consistency, was added to a flaskwith an off-gas system as described in Example 4 and heated to 155 C. atmm. Hg absolute vacuum over 2 /3 hours to yield 40.5 parts of a whitesolid. During this heating period 7.3 parts of water were recovered. Aportion of the white solid (1.8062 parts) was gradually heated in aquartz tube with a nitrogen blanket as in Example 3 to 700 C. over a3-hour period and held at the latter temperature for 1 hour, whereupon0.3190 part of residue was recovered which analyzed 26.7% boron and46.4% nitrogen. A portion of the residue (0.2303 part) was then heatedin a stream of ammonia gas to 800850 C. for 2 hours according to theprocedure of Example 4 and 0.1479 part of a white boron nitride wasrecovered which analyzed 41.4% boron and 50.7% nitrogen. The X-rayditfraction pattern of this material was that of turbostratic boronnitride.

Example 6 According to the procedure of Example 3, 68.0 parts ofaminoguanidine bicarbonate and 15.4 parts of boric acid were mixed andadded to a flask as described in EX- ample 4. This mixture was heated to126 C. over a 3- hour period under 5 mm. Hg absolute pressure to yield43.1 parts of a solid residue. A portion of the residue (3.4410 parts)was added to a quartz tube with a nitrogen blanket as described inExample 3 and heated from 200 to 800 C. over a period of 2 hours. Thenitrogen flow through the tube was stopped and ammonia gas was fedthrough the tube while the heat was increased to 900 C. for anadditional 3 hours. After purging and cooling as described in Example 3,0.4893 part of a white boron nitride was recovered which analyzed 41.4%boron and 44.1% nitrogen.

The X-ray diffraction pattern of this material was that of tur-bostraticboron nitride.

Example 7 a pressure of 5 mm. Hg absolute. Some water was evolved aroundC. The resulting solid (88.0 parts) was charged to a quartz tube asdescribed in Example 3 and the tube was heated to approximately 700 C.over a period of about 4 hours, whence the nitrogen flow was stopped andammonia gas was fed through the bed at 700 C.950 C. for approximately 3hours. A white residue of boron nitride which analyzed 40.5% boron and49.0% nitrogen was recovered after purging the tube with nitrogen afterthe ammonia treatment and cooling. The X-ray diifraction pattern of thismaterial was that of turbostratic boron nitride.

Example 8 A mixture obtained by pulverizing 31.5 parts of melamine and17.2 parts of orthoboric acid was added to .a flask equipped asdescribed in Example 4. The mixture .After cooling, 44 parts of solidresidue were obtained and it was noted that 4.5 parts of water had beenevolved. A portion of this residue (23.6 parts) was charged to a quartztube as described in Example 3 and heated to 900 C. in a stream ofnitrogen over a 5-hour period with the temperature over 500 C. for atleast 2 hours of heating. The nitrogen stream was then discontinued andammonia gas was passed through the tube which was held at 800- 950 C.for 4 hours. After purging the tube with nitrogen and cooling, 3.3 partsof colorless residue, boron nitride, were recovered which analyzed 42.5%boron and 50.2% nitrogen. The X-ray diffraction pattern of this materialwas that of turbostratic boron nitride.

Example 9 Into a flask, equipped as described in Example 4, was charged41.3 parts of cyanuric acid and 15.5 parts of orthoboric acid which hadbeen mixed by pulverization. This mixture was heated to 200 C. over a2-hour period at a pressure of 7 mm. Hg absolute and upon cooling 55.6parts of residue and 4.7 parts of water were recovered. A portion of thesolid residue (26.7 parts) was placed in a quartz tube and the tube washeated to 300 C. over a 1-hour period while a stream of nitrogen waspassed therethrough. The stream of nitrogen was discontinued and astream of ammonia gas was started, the tube was heated to 900 C. over a3-hour period and maintained at 900-950 C. in a stream of ammonia for anadditional 4 hours. After purging the tube with nitrogen followed bycooling 2.7 parts of a white boron nitride residue was recovered whichanalyzed 41.1% boron and 48.8% nitrogen. The X-ray diffraction patternof this material was that of turbostratic boron nitride.

Example 10 Into a flask, equipped as described in Example 4, was charger128.1 parts of ammelide and 30.9 parts of boric acid which had beenmixed by pulverization. This mixture was heated to C. over a 1.7-hourperiod with the final heating being effected at a pressure of 2 mm. Hgabsolute and upon cooling 154.3 parts of residue and 4 parts of waterwere recovered. A portion of the solid residue (1.7075 parts) was placedin a quartz tube and the tube was heated to 500 C. over a 3-hour periodwhile a stream of nitrogen was passed therethrough. The stream ofnitrogen was discontinued and a stream of ammonia gas was started,whence the tube was heated to 950 C. over a 3.33-hour period andmaintained at about 950 C. in the stream of ammonia for an additional 3hours. After purging the tube with nitrogen followed by cooling, 0.1332part of a white boron nitride residue was recovered which analyzed 50.6%

nitrogen. The X-ray dilfraction pattern of this material was that ofturbostratic boron nitride.

Example 1] Into a flask, equipped as described in Example 4, was charged45 parts of guanidine carbonate and 30.9 parts orthoboric acid. Themixture was then treated with 30 ml. of glacial acetic acid to convertthe guanidine carbonate to guanidine acetate. After the evolution ofcarbon dioxide had ceased the mixture was heated to 150 C. over a 2-hourperiod with heating above 114 C. being eifected at a pressure of 2 mm.Hg absolute and upon cooling 75.8 parts of residue were recovered. Aportion of the solid residue (2.1091 parts) was placed in a quartz tubeand the tube was heated to 500 C. over a 3-hour period while a stream ofnitrogen was passed therethrough. The stream of nitrogen wasdiscontinued and a stream of ammonia gas was started whence the tube washeated to 950 C. over a 3.3-hour period and maintained at about 950 C.in the stream of ammonia for an additional 2 hours. After purging thetube with nitrogen followed by cooling, 0.3223 parts of a white boronnitride residue amounting to a yield of 93.4% based upon the boric acidoriginally charged was recovered which analyzed 54.3% nitrogen. TheX-ray diffraction pattern of this material was that of turbostraticboron nitride.

Example 12 :Into a flask, equipped as described in Example 4, wascharged 10.0 parts of urea, 15.0 parts of guanidine carbonate, 12.7parts of thiourea, and 30.9 parts of orthoboric acid which had beenmixed by pulverization. This mixture was heated to 220 C. over a 2-hourperiod with the heating above 100 C. being conducted at a pressure of 2mm. mercury absolute and upon cooling 46.4 parts of residue and 14.8parts of water were recovered. A portion of the solid residue (2.209parts) was placed in a quartz tube and the tube was heated to 500 C.over a 3-hour period while a stream of nitrogen was passed therethrough.The stream of nitrogen was discontinued and a stream o-f ammonia gas wasstarted whence the tube was heated to 950 C. over a 3.3 l-hour periodand maintained at about 950 C. in the stream of ammonia for anadditional 3 hours. After purging the tube with nitrogen followed bycooling, 0.6418 part of a white boron nitride residue were recoveredwhich analyzed 51.8% nitrogen. The X-ray diffraction pattern of thismaterial was that of turbostratic boron nitride.

This example shows that a mixture of the compounds are workable in theprocess of this invention.

Example 13 Turbostratic boron nitride (3.9 grams) made by the process ofExample 1 was placed in an open weighed ceramic boat. The boat and itscontents were then placed in a horizontal carbon resistance furnace andheated over a 3-hour period in a stream of dry nitrogen to a temperatureof 1330 C. The temperature of the boat and its contents was recorded bydirect sighting with a calibrated optical pyrometer. The boat andcontents were kept at 1330 C. for 2 hours. The temperature was thenincreased to 1400 C. and maintained at this temperature for 2 hours.Then the temperature was increased to a final temperature of 1550 C.over a final l-hour heating. Heating was then: discontinued and the boatand contents cooled in the nitrogen stream. A

white solid (3.4 grams) was recovered.

The X-ray diffraction pattern of this material was that of turbostraticboron nitride, with no evidence of the development of three-dimensionalorder.

Example 14 Turbostratic boron nitride powder (28 grams) which had beenprepared according to the process of Example 1 was placed in a graphitemold and heated under pressure. The mold cavity consisted of a hollowcylinder of 2-inch diameter. Pressure was applied to the boron nitridepowder in the mold by means of a graphite piston, connected to ahydraulic pressure system capable of exerting a finely controlledpressure. The graphite mold and its contents were bathed in a stream ofdry nitrogen during the heating and subsequent cooling. Heat wassupplied to the graphite mold by means of an induction coil, connectedto a high-frequency power converter. The temperature of the graphitemold, as recorded by an optical pyrometer, was raised to 1700 C. Duringthis heating period the pressure in the mold was 3000 psi. The materialin the mold was maintained under 3000 psi. pressure at 1700 C. for 30minutes. At the end of this period, heating was discontinued and thecontents of the mold allowed to cool to room temperature. Pressure wasthen removed and the mold opened.

A white, compacted, cylindrical chip resulted. The X-ray diffractionpattern of this material was that of turbostratic boron nitride, with noevidence of the development of three-dimensional order.

Example 15 Turbostratic boron nitride (1.2 grams), prepared according tothe method of Example 1, was mixed with vanadium oxide (V 0 (4.12grams). The mixture was pulverized with an agate pestle and mortar. Aportion o-f the pulverized mixture (2.4 grams) was then placed in aloosely covered ceramic 'boat and the boat and its contents were thenheated in a stream of dry nitrogen within a carbon resistance furnace.The ceramic boat and cover were made by machining a. piece of boronnitride ceramic. Prior to use in this experiment, the boat and cover hadbeen slowly heated several times in a stream of dry nitrogen, to a finaltemperature of 2300" C., until the boat and cover showed no furtherweight loss on heating. The boat and reaction mixture were heated to 950C. over a 20-minute period. The temperature was then slowly raised sothat a temperature of 1600 C. was attained after 3 hours and a finaltemperature of 2000 C. was reached after a total heating time of about 8hours. Heating was then discontinued and the boat and its contentscooled in the stream of nitrogen. A black residue (2.1 grams) ofneedle-like crystals remained in the boat. X-ray analysis of thesecrystals positively identified the material as vanadium diboride, VB

Example 16 A portion (2.6 grams) of a mixture composed of turbostraticboron nitride (1.5 grams) prepared according to the method of Example 1and tungsten oxide, W0 (3.45 grams) was heated in a stream of nitrogen,as in Example 8. The following heating schedule was employed:

Temperature, C.: Time Room temperature- 1000 15 minutes. 10001400 2hours.

1400 4 hours, 40 minutes.

On cooling, a residue (2.4 grams) remained in the boat. The residue wasidentified by X-ray analysis as tungsten metal with a minor portion ofunreacted boron nitride.

Example 17 A portion (1.9 grams) of a mixture of turbostratic boronnitride (2.4 grams) made according to the procedure of Example 1 andniobium oxide (2.65 grams) was heated in a stream of nitrogen as inExample 15 according to the following schedule:

Temperature, C.: Time Room temperature- 1200 minutes 15 1200-1400 hours2 1400-1500 hour /2 1500-1700 hours 2 1700 do 2 17 A residue (1.0 gram)of black material identified as 5 niobium boride, Nb B and a minoramount of unreacted components remained in the boat.

Example 18 A portion (5.0 grams) of a mixture of turbostratic boronnitride (2.4 grams) prepared according to Example 1 and zirconium oxide(6.15 grams) was heated, as in Example 15, in a stream of dry nitrogenaccording to the following schedule:

Temperature, C.: Time Room temperature-+1000 minutes 20 1000-1400 hours2 1400-1700 do 2 1700-1800 hour 1 1800 hours 3 After cooling, a blackresidue (2.6 grams) remained. This was identified as a mixture of azirconium diboride phase and a solid solution of zirconium nitride andzirconium boride.

Example 19 A portion (3.65 grams) of a mixture of turbostratic boronnitride prepared according to Example 1 (0.96 gram), and molybdenumoxide, M (2.88 grams), was heated in a stream of dry nitrogen to 1500 C.over a 1- hour period and then held at 1500 C. for a further period of 4hours. The reaction mixture was contained in a boron nitride ceramicboat, and the heating was achieved by means of a carbon resistancefurnace, as in the preceding examples.

After cooling, a residue (275 grams) remained. This was identified byX-ray analysis as a mixture of molybdenum metal, aMO B and some MoB.

Example 20 A portion of a mixture of turbostratic boron nitride (1.2grams) prepared according to Example 1 and tantalum oxide, Ta O (2.2grams) was heated in a stream of dry nitrogen for 7 hours at 1600 C. Thesample was contained in a boron nitride ceramic boat which was heatedwithin a carbon resistance furnace. After cooling, 0.5 gram of residueremained. X-ray analysis revealed the residue to be essentially pureATaB.

Another portion of the mixture, heated to 2000 C. for 4 hours in astream of nitrogen, yielded TaB as the main reaction product.

Example 21 A portion (2.1 grams) of a mixture of turbostratic boronnitride (2.0 grams) made according to the method of Example 1, andnickel oxide, Ni O (2.12 grams) was heated for 11 hours at 1400 C. in astream of helium gas. A residue (1.5 grams) was recovered which wasshown on analysis to be a mixture of elemental nickel and some boronnitride with a fully developed, three-dimensional, crystalline lattice.

Example 22 Turbostratic boron nitride (6.2 g.), which was pre- .pared bythe reaction of urea with boric acid and ammonia, and which on analysiswas found to contain 45.2% N, 41.6% B, was mixed with aluminum oxide(10.2 g.) and the mixture was then pulverized with an agate pestle andmortar.

Portions of the mixture (2.2 g. and 3.1 g, respectively) were thenplaced in open ceramic boats. (Each boat was machined from a solid pieceof ceramic boron nitride.) Prior to use, each boat had been fired toconstant weight at 2300 C. in a stream of nitrogen. The boats were thenplaced inside a carbon resistance furnace and heated in a stream of drynitrogen. The position of the boats was such that the boat which wasupstream relative to the N flow was :fully within the maximum uniformtemperature zone, which was about 5" in length, while the downstreamboat was partly within the maximum temperature zone and partly in adescending temperature gradient on the downstream side of the maximumtemperature zone. An inner sleeve of boron nitride ceramic was insertedinto the furnace in the space between the boats and the vent from thefurnace, to collect any materials that might deposit in the cooldownstream segment of the furnace during the experiment.

The temperature of the furnace (maximum temperature) was then raisedaccording to the following schedule:

Temperature, C.: Time, hours The furnace was then allowed .to cool.

The upstream boat, which originally contained 2.2 g. of the mixture,contained 0.1 g. of a white residue. Analysis of the residue indicatedthis material to be fully crystalline boron nitride. The downstreamboat, which originally contained 3.1 g. of the mixture, now contained1.5 g. residue. The contents of this boat showed a temperature gradientetfect. Very little material remained in that portion of the boat whichhad been in the maximum temperature zone, but the amount of residueshowed a progressive increase in the portion of the boat that lay in thetemperature gradient. Furthermore, in this portion of the boat there wasa surface layer of transparent, crystalline material. Examination ofthis crystalline material by X-ray analysis revealed it to be aluminumnitride. X-ray analysis indicated that the other components of theresidue in the downstream boat were fully crystalline boron nitride and1 -Al O A deposit of transparent, fine needles collected on the boronnitride inner sleeve. Examination of this material by X-ray showed it tobe essentially 9Al O -2B O The nitrogen content of the purer productsobtained by the process of the present invention indicates virtuallypure boron nitride even though the theoretical percent N for BN is 56%;this is possibly because of the low values generally obtained inKjelda-hl analyses of BN due to the limitation of the analytical method.The purest commercial boron nitrides, analyzed by the same procedure,give Kjeldahl values of about 48 %52%.

The invention is highly useful in that it provides a greatly improvedmethod for making a product of established utility and in that itbroadens the field of utility for boron nitride by reducing the cost ofproducing same. In this connection, it is, of course, to be noted thatthe invention is not restricted to the compounds mentioned herein, sincethe intermediate products in the practice of the invention areoxygen-containing condensation products of boric acid and anitrogen-containing compound. This is desirable because theseintermediates do not require the use of solid supports, or washing stepswhich characterize earlier processes for making boron nitride productsby the use of ammonia as the source of nitrogen.

The invention claimed is:

1. A process for the production of metal nitrides, said processcomprising admixing turbostratic boron nitride and the oxide of a metalselected from the group consisting 3,261,667 19 20 of aluminum,titanium, and zirconium; heating said mix- References Cited by theExaminer ture to above 1000" C.; and recovering the corresponding metalnitride from said mixture.

2. A pnocess for the production of metal borides, said processcomprising admixing rturbostratic boron nitride 5 and the \OXldC of ametal selected from the group con- OSCAR VERTIZ, Primary Examine!-sisting of zirconium, vanadium, niobium, chromium, MA BRINDISI, BENJAMINHENKIN, molybdenum, and tantalum; heating said mixture to aboveExamingrs 1000 and recovering the corresponding metal boride 10 L J.BROWN Assistant Examiner from said mixture.

Mellor Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 8, :page 111 (1928).

1. A PROCESS FOR THE PRODUCTION OF METAL NITRIDES, SAID PROCESSCOMPRISING ADMIXING TURBOSTRATIC BORON NITRIDE AND THE OXIDE OF A METALSELECTED FROM THE GROUP COMPRISING OF ALUMINUM, TITANIUM, AND ZIRCONIUM;HEATING SAID MIXTURE TO ABOVE 1000*C.; AND RECOVERING THE CORRESPONDINGMETAL NITRIDE FROM SAID MIXTURE.
 2. A PROCESS FOR THE PRODUCTION OFMETAL BORIDES, SAID PROCESS COMPRISING ADMIXING TURBOSTRATIC BORONNITRIDE AND THE OXIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OFZIRCONIUM, VANADIUM, NIOBIUM, CHROMIUM, MOLYBDENUM, AND TANTALUM;HEATING SAID MIXTURE TO ABOVE 1000*C.; AND RECOVERING THE CORRESPONDINGMETAL BORIDE FROM SAID MIXTURE.